Method of inhibiting corrosion of metals



ited

METHOD OF INHIBITING CORROSION F NETALS' No Drawing. Application June 13, 1952, Serial No. 293,454

5 Claims. (Cl. 252-855) This invention relates to inhibiting corrosion of metals, and more particularly to improved processes for the prevention of corrosion in natural gas collection and distribution systems.

In the production of natural gas, and especially when the producing wells are high pressure wells of the type generally known as gas-condensate wells, some water, along with condensable hydrocarbon fluids, tends to condense out of the gas and coat the walls of, the gathering and distribution lines. When carbon dioxide or traces of organic acids are present in the gas as is generally the case, they tend to dissolve in the condensed water to form highly corrosive solutions which rapidly eat their way through the lines.

Various methods have been proposed in the past for controlling this type of corrosion. In larger systems such as main gas lines it has sometimes beenfoun'd profitable to install gas dryers, but the expense of installing such dryers is usually prohibitive in smaller systems, especially in gas collecting lines where the corrosion problem is most acute. In such lines certain chemical inhibitors have found to be of some use, but even the best of the inhibitors now commercially available have not proven entirely satisfactory. While they do reduce corrosion to some extent, even with their use corrosion continues to such an extent as to pose a serious economic problem.

We have now discovered that if certain oxazolidines formed by the reaction of equimolar quantities of monoor diethanol amine with a carbonyl compound having from two to seven carbon atoms is introduced into the pipelines, that corrosion can be reduced to ten percent or less of that which would be suflered in uninhibited operations, even when the quantity of oxazolidine present is tes Patent" 0 only in the neighborhood of parts per million, based on the amount of water present in the lines. These oxazolidine compounds have the generic formula in which R is an alkyl radical having from one to six carbon atoms, R may be hydrogen or an alkyl radical, depending on whether the azolidine is produced from an aldehyde or a ketone, and provided that the sum of the carbon atoms of R and R, shall not exceed 6, and R" may be hydrogen or an ethanol radical, depending on whether monoor diethanol amine is used as a starting material. Such compounds, and the method of making them, are Well known to the art. For example, they are described in German Patent 564,787, to I. G. Farben.

In order to test these compounds, and to compare their effectiveness with presently commercially available inhibitors a testing procedure was set up designed to duplicate as closely as possible in the laboratory the corrosive conditions existing in gas collection lines. In this testing procedure 800 ml. of distilled water which had been 2,737,491 Patented Mar. 6, 1956 boiled to exclude as much oxygen as possible was placed in a one quart bottle and'was acidified with 0.05% by weight of acetic acid- Dry Ice in excess of. that required to saturate the water wasthen placed in the bottle, inhibitor inthe amount of 50 parts per million was added, except in the case of the blank tests, and a tared hot rolled steel test strip suspended on a. glass hook from a rubber stopper was introduced. The bottle was then capped and allowed to stand for two weeks at room temperatures. At the end of this time the strip was withdrawn, cleaned in dilute hydrochloric acid, dried, and reweighed.

: Results of representative tests are shown in the following table. Tests A and B were run at different times, and the slight 'diiference in weight loss in the blank test strips is no doubt due to slight dilferences in the ambient tem-' peratures during the tests. Commercial inhibitors A and B are commercial products especially recommended by the manufacturers for inhibiting corrosion in wet gas lines, andhave proven in use to be the best inhibitors commercially available. Inhibitor X1 is the oxazolidine reaction product of diethanol amine and heptaldehyde; X2 that of monoethanolamine and heptaldehyde; X3 that of monoethanolamine and acetaldehyde; and X4 that of diethanolamine and acetaldehyde.

Table 1 TEST A Weight Percent Inhibitor gf g g protection It will be observed from the foregoing that our new inhibitors exhibit remarkable efiiciency in combatting corrosion, and are far superior to either of the commercial inhibitors. It appears essential to outstanding performance that the carbon connecting the nitrogen and oxygen atoms of the oxazolidine ring be substituted by at least one alkyl group. While unsubstituted oxazolidines show considerable effectiveness as corrosion inhibitors, they are not the equals of those claimed herein. For example, during Test A, oxazolidines formed from monoethanolamine and formaldehyde, and diethanol amine and formaldehyde were also tested, and showed protection percentages of 78.9 and 58.0 respectively. While this protection is comparable to that obtained by presently available commercial inhibitors, it will be observed that when using a corrosion inhibitor giving a protection percentage of 78.9, the corrosion is more than twice as great as when using a corrosion inhibitor having a protection percentage of 89.6, the least eilicient of our preferred compounds.

We have also found that the chain length of the carbonyl compound reacted with the ethanol amine should be under eight carbon atoms, since the oxazolidines formed using carbonyls of greater chain length do not have sufiicient water solubility to be useful in our process.

It will be apparent that while an inhibitor concentration of 50 p. p. m. was established as a test standard for comparison purposes, more or less inhibitor may be used, depending on the corrosiveness of the aqueous phase present in the gas lines. In actual use in the field the concentration must, of course, be adjusted to the particular conditions there obtaining, provided only that the inhibitor'is introduced in a small but sufficient amount to substantially inhibit corrosion. We find that excellent results are obtained by dissolving the inhibitor in an appropriate amount of water, in order to better control the amount of inhibitor used, and injecting the inhibitor solution into the gas lines as near to the well head as possible. The gas current flowing through the lines is then effective to mix the inhibitors with the corrosive fluids present, and to sweep the inhibitor throughout the system, affording protection to all metal equipment with which it comes in contact downstream of the point of injection.

The nature of the inhibiting action of our new inhibitors is not fully understood, but, since they are not introduced in quantities sufficient to neutralize acidic materials present, apparently they must form some sort of film on the surface of the metal, thus excluding corrosive fluids from contact therewith. In any event, however, no matter what the mechanics of the corrosion control may be, they are extremely and surprisingly effective in reducing corrosion even when used in minute quantities.

Having now described our invention, What is claimed l. The process of reducing the corrosion of metals when exposed to the corrosive action of aqueous solutions having dissolved therein acidic materials selected from the group consisting of water soluble organic acids and carbon dioxide which comprises incorporating into said aqueous solutions a small quantity but sufficient to substantially inhibit corrosion, of an inhibitor having the generic formula in which R is an alkyl radical having less than seven carbon atoms, R is a radical selected from the group consisting of hydrogen and alkyl radicals, provided that the total carbon atoms in R and R shall not exceed 6, and R" is a radical selected from the group consisting of hydrogen and ethanol, and thereafter causing the inhibitor to flow in contact with the metal to be protected.

2. The process according to claim 1 in which the inhibitor has the formula CHrO N C-CH;

3. The process according to claim 1 in which the inhibitor has the formula 4. The process according to claim 1 in which the inhibitor has the formula 5. The process according to claim 1 in which the inhibitor has the formula References Cited in the file of this patent UNITED STATES PATENTS 

1. THE PROCESS OF REDUCING THE CORROSION OF METALS WHEN EXPOSED TO THE CORROSIVE ACTION OF AQUEOUS SOLUTIONS HAVING DISSOLVED THEREIN ACIDIC MATERIALS SELECTED FROM THE GROUP CONSISTING OF WATER SOLUBLE ORGANIC ACIDS AND CARBON DIOXIDE WHICH COMPRISES INCORPORATING INTO SAID AQUEOUS SOLUTIONS A SMALL QUANTITY BUT SUFFICIENT TO SUBSTANTIALLY INHIBIT CORROSION, OF AN INHIBITOR HAVING THE GENERIC FORUMLA 